I experimented with a number of different oils in my motorcycle a few years ago.
RP did not maintain viscosity any better than Castrol GTX. Mobil-1 and Amsoil held grade for 6000 miles. RP dropped from 20w50 to a 30wt in 2000 miles.

RP spends more money on marketing and product placement on TV shows than they do on developing a good product.

You can always vary the weight, it's a trade-off between pumpability and film coverage. Now, for maintaining warrantee, and proof, you should stick with the recommended, outside of this, it's what fits your needs.